This application relates generally to rotary machines and more particularly, to methods and apparatus for sealing rotary machines.
At least some known rotary machines such as, but not limited to steam turbines or gas turbines, include a plurality of seal assemblies in a fluid flow path to facilitate increasing the operating efficiency of the rotary machine. For example, some known seal assemblies are coupled between a stationary component and a rotary component to provide sealing between a high-pressure area and a low-pressure area. Moreover, to facilitate thrust balancing, a turbine rotor may be sealed relative to a cooperating stator to facilitate maintaining a higher pressure in a forward portion of the rotor as compared to a lower pressure in an aft portion of the rotor.
At least some known seal assemblies include seal members such as, but not limited to, brush seals, labyrinth seals, and/or compliant plate seals. Compliant plate seals generally include a plurality of compliant plates such as, but not limited to, leaf seals, shingles seals, tapered plate seals, laby-plate seals, and/or intermediate plate seals, that are oriented in a pack extending circumferentially about a central rotational axis of a rotary component. More specifically, the plates are oriented such that a tip of each plate contacts the rotor or rotary component during various operating conditions of the rotary machine. For example, during shut down of the turbine engine, a portion of the plates are generally in contact with a rotary component. During rotation of the rotary component, various forces such as compliant plate/rotor contact forces, hydrodynamic lifting forces, and differential pressure forces cause the plates to deflect upward. Compliant plate/rotor contact forces are generated as a result of contact between the compliant plate and the rotary component. Hydrodynamic lifting forces are generated by rotation of the rotary component. Differential pressure forces include radially outward lifting forces and radially inward blow-down forces that are generated due to the static pressure distribution on the compliant plates. A balance between preventing contact between the compliant plate tips and the rotor, and preventing seal leakage is desirable to increase the life-span of the compliant plates and to increase the efficiency of the rotary machine.
Some known seal assemblies include a seal housing that includes a high-pressure-side front wall and a low-pressure-side rear wall that is spaced a distance from the front wall such that a cavity is defined therebetween. In such seal assemblies, the gap between the compliant plates and the front wall, and the gap between the compliant plates and the rear wall, are each defined based on the positional mounting of the compliant plates within the cavity. Known seal assemblies are generally assembled in an attempt to ensure known gap widths are defined between the seal housing and the compliant plates.
Generally, variations in sizes of the physical gaps may influence the magnitude of forces exerted on the compliant plates and as such may adversely impact the ability of the plates to prevent axial flow leakage through the seal assemblies. In some known seal assemblies, the size and/or configuration of the front and rear gaps enable lifting forces or blow-down forces to impact the compliant plates. The size and/or configuration of the physical gaps, in some known seal assemblies, are fixed and as a result, such designs limit the control of the forces exerted on the compliant plates. For example, depending on the forces exerted during operation, the compliant plate tips may contact the rotor during shut down of the rotary machine, which may undesirably reduce the life-span of the compliant plates and/or the efficiency of the rotary machine.